The present invention is directed to a rod coil for ignition systems, in particular in the form of an ignition coil in internal combustion engines of motor vehicles according to the definition of the species in claim 1.
A rod coil having a cylindrical housing in the basic form is known from German Patent 196 23 399 C2. A rod-shaped core of an open magnetic circuit is centrally located in the housing and within a winding set. To control the magnetic field, the winding set is concentrically surrounded by a sleeve-shaped slotted yoke mounted on an inner wall or, alternatively, on an outer wall of the housing, an insulator being inserted in between. The purpose of this yoke is to close the magnetic field of the rod coil.
Due to unavoidable, production-related dimensional inaccuracies in the yoke and housing, air-filled cavities are produced between the two bodies when the yoke comes to rest against the housing. Partial electrical discharges that, over the long term, cause deterioration of the rod coil insulation through material wear, possibly resulting in coil failure, occur at these voids during rod coil operation.